Field of the Invention
Embodiments disclosed herein relate generally to apparatuses and methods for determining fluid rheology. More specifically, embodiments disclosed herein relate to apparatuses and methods for automatically determining fluid rheology at a drilling or waste injection location. Additionally, embodiments disclosed herein relate to apparatuses and methods for determining fluid rheology using Marsh funnels and Simplex Method algorithms.
Background Art
When drilling or completing wells in earth formations, various fluids typically are used in the well for a variety of reasons. Common uses for well fluids include: lubrication and cooling of drill bit cutting surfaces while drilling generally or drilling-in (i.e., drilling in a targeted petroliferous formation), transportation of “cuttings” (pieces of formation dislodged by the cutting action of the teeth on a drill bit) to the surface, controlling formation fluid pressure to prevent blowouts, maintaining well stability, suspending solids in the well, minimizing fluid loss into and stabilizing the formation through which the well is being drilled, fracturing the formation in the vicinity of the well, displacing the fluid within the well with another fluid, cleaning the well, testing the well, transmitting hydraulic horsepower to the drill bit, fluid used for emplacing a packer, abandoning the well or preparing the well for abandonment, and otherwise treating the well or the formation.
Drilling fluid takes the form of a “mud,” i.e., a liquid having solids suspended therein. The solids function to impart desired rheological properties to the drilling fluid and also to increase the density thereof in order to provide a suitable hydrostatic pressure at the bottom of the well.
Drilling fluids are generally characterized as thixotropic fluid systems. That is, they exhibit low viscosity when sheared, such as when in circulation (as occurs during pumping or contact with the moving drilling bit). However, when the shearing action is halted, the fluid should be capable of suspending the solids contained therein to prevent gravity separation. In addition, when the drilling fluid is under shear conditions and a free-flowing near-liquid, it must retain a sufficiently high viscosity to carry all unwanted particulate matter from the bottom of the well bore to the surface. The drilling fluid formulation should also allow the cuttings and other unwanted particulate material to be removed or otherwise settle out from the liquid fraction. This is also true for solid waste (i.e., drill cuttings) slurry injection operations. That is, the slurry must have adequate rheological properties to suspend and carry the cuttings and/or other solid particles to avoid settling and thus loss of injectivity of the injection well.
There is an increasing need for drilling fluids having the rheological profiles that enable wells to be drilled more easily. Drilling fluids having tailored rheological properties ensure that cuttings are removed from the wellbore as efficiently and effectively as possible to avoid the formation of cuttings beds in the well which can cause the drill string to become stuck, among other issues. There is also the need from a drilling fluid hydraulics perspective (equivalent circulating density) to reduce the pressures required to circulate the fluid, reducing the exposure of the formation to excessive forces that can fracture the formation causing the fluid, and possibly the well, to be lost. In addition, an enhanced rheological profile is necessary to prevent settlement or sag of the weighting agent in the fluid. If this occurs it can lead to an uneven density profile within the circulating fluid system which can result in well control (gas/fluid influx) and wellbore stability problems (caving/fractures).
In waste (e.g., drill cuttings) injection operations, if the cutting slurry does not have adequate solid suspension capacity, the solids (i.e., drill cuttings) may settle out of the slurry and accumulate at the bottom of the well, and the injection well may become inoperable from loss of injectivity. This can happen in a matter of hours, and therefore, real-time measuring of the slurry or fluid during drill cuttings or solid waste slurry injection operations should be considered when performing such operations.
To obtain the fluid characteristics required to meet these challenges the fluid must be easy to pump, so it requires the minimum amount of pressure to force it through restrictions in the circulating fluid system, such as bit nozzles or down-hole tools. In other words the fluid must have the lowest possible viscosity under high shear conditions. Conversely, in zones of the well where the area for fluid flow is large and the velocity of the fluid is slow or where there are low shear conditions, the viscosity of the fluid needs to be as high as possible in order to suspend and transport the drill cuttings. This also applies to the periods when the fluid is left static in the hole, where both cuttings and weighting materials need to be suspended to prevent the settlement thereof. However, it should also be noted that the viscosity of the fluid should not continue to increase under static conditions to unacceptable levels. Otherwise when the fluid needs to be circulated again, this can lead to excessive pressures that can fracture the formation or lead to lost time if the force required to regain a fully circulating fluid system is beyond the limits of the pumps.
In order to determine the rheology of a particular fluid, various field techniques have been used. For example, viscometers have been used to determine the viscosity of fluids in the field; however, such methods of determining viscosity are often slow and require manual attention. Other times, drilling fluid engineers or injection engineers are dispatched to drilling or waste injection locations to take manual measurements of fluids used in a drilling or solid waste slurry injection operation in order to determine the properties of specific drilling fluids or solid waste slurries; however, such methods are often expensive and are not convenient for real-time measurement, depending on the drilling or injection location.
Accordingly, there exists a continuing need for apparatuses and methods for determining fluid rheology in real-time.